The major goals of this proposal are to identify and characterize the ionic currents in smooth muscled muscularis mucosae of the gastrointestinal tract, to study their physiological role and their modulation by putative neurotransmitters. To achieve these aims, electrophysiological studies will be carried out in the whole tissue using high resistance microelectrodes to identify the excitatory and inhibitory potential changes, and the ionic currents will be studied in single cells using the patch clamp technique. Macroscopic currents will be characterized in the whole cell voltage clamp mode, and the single channels will be further examined using cell-attached and excised patch recording techniques. Specifically, the role of the K+ and the C1- channels involved in resting transmembrane potential and in excitatory potential induced by acetylcholine and substance P and inhibitory potentials by VIP, nitric oxide and ATP will be examined. Studies will be performed in esophageal muscularis mucosae and compared with intestinal and gastric muscularis mucosae in order to define the heterogeneity of K+ and C1- channels. These ions play a key role in the resting and the agonist-induced modulation of the membrane potential. The study on the K+ channels will include the large conductance charybdotoxin-sensitive Ca2+-activated K+ channel, the smaller conductance apamin and [ATP]o-sensitive Ca2+-activated K+ channel and the glybencamide and [ATP]i-sensitive K+ channel. The study on C1- channels will include the Ca2+-activated C1- channel, the maxi C1- channel and the background C1- channel. These studies will be performed in rats, rabbits, guinea-pigs and discarded human gastrointestinal tissues. The results from these studies will help define the ionic basis of the activity of the muscularis mucosae which may play a crucial role in the motor as well as secretory and absorptive functions in the gastrointestinal tract.